[2024] "Strange Cloud authentication with user token failed with error"

Can you post the full log?

How exactly do you start the server?

That sounds like a connectivity issue, for that see the first point in this thread, it applies to that as well: https://steamcommunity.com/app/382310/discussions/4/4701287772393189498/

How you can find the logs is explained here: https://github.com/StrangeLoopGames/EcoIssues/wiki/Getting-the-Eco-server-and-client-log-files-for-local-world

Note that what we need in this case is the server logs.